When I set up my troops and go to click the Engage button for battle, it's not available. It's grayed out so to speak. However, if I choose the auto function in the bottom left then the battle plays out automatically just fine.
Both times I clicked the auto option it left my troops designation the same as I had put them. However when I hover the mouse over the Engage button it tells me that I have not committed properly, but I have. I've used this battle menu hundreds of times through the years so I'm no dummy to it. Well, maybe a dummy but not with the battle menu.

Attached is the saved picture with the tooltip showing the commitment being wrong.